Magnetizing and erasing head arrangement for magnetic recorders



April 8, 1947. c s 2,418,542

MAGNETIZING AND ERASING HEAD ARRANGEMENT FOR MAGNETIC RECORDERS Filed Jan. 20, 1944 2 Sheets-Sheet l Eq-z 3 j I F/ 3 M 7 5 Q /2J I l l-/4 fly April 8, 1947. M. CAMRAS 2,418,542 MAGNETIZING AND ERASING HEAD ARRANGEMENT. FOR MAGNETIQ RECORDERS Filed- Jan. 20, 1944 2 Sheets-Sheet 2 Patented Apr. 8, 1947 MAGNETIZING AND ERASING AR- RAN GEMEN T FOR MAGNETIC RECORDERS Marvin Camras, Chicago, IlL, assignor to Armour Research Foundation, Chicago, 111., a corporation of Illinois Application January 20, 1944, Serial No. 518,922

This invention relates to improvements in a magnetic recording and reproducing device, and more particularly to a magnetizing and erasing head arrangement for magnetic recorders, although the invention may have other uses and purposes as will be apparent to one skilled in the art.

In many instances in connection with magnetic recording devices, it is desirable to employ an erasing head in addition to the recording head so as to insure what may be termed a clean wire before the recording head acts upon that wire. Such arrangement also eliminates the necessity of demagnetizing the recording medium, which may be in the form of a paramagnetic wire, tape, or other elongated element, at some location remote from the recording device. When an erasing head is employed, a medium magnetized in accordance with a previous recording may be used, and the erasing head will remove that previous recording prior to the medium reaching the recording head. In compact recording devices, however, it has been found difficult to provide both the erasing head and recording head because of insufficient room to accommodate them. In many arrangements, it is necessary to place the recording head and erasing head very close together, and yet it is desirable to provide a source of high frequency current for both the erasing head and recording head.

With the foregoing in mind, it is an important object of the instant invention to provide a magnetic recording and reproducing device wherein no high frequency current is applied to the recording head, and yet the benefits of such an application of high frequency are obtained in the recording head.

Another object of the invention resides in the provision of an erasing head and recording head arrangement for a magnetic recording device such that the high frequency component desired in the recording head issupplied by stray high frequency flux from the erasing head.

A further object of the instant invention resides in the provision of an erasing head and magnetizing head for a magnetic recorder in the form of a unitary assembly, both heads utilizing the same core, and the high frequency component in the recording head being obtained by virtue of stray flux from the erasing head.

Still another object of the instant invention is the provision of a recording and reproducing head for a magnetic recording device to which only audio-frequency current is supplied. but the arrangement being such that the recording pos- .12 Claims. (01479-1002) sesses all benefits of the added application of high frequency current.

Also an object of the invention is the provision of a recording head arrangement for a magnetic recording device especially designed to lessen wear on the head by the recording medium travelling thereby.

Still a further object of the instant invention resides in the provision of an erasingand record; ing head assembly for a magnetic recording device so arranged as to permit the wire to travel in either direction by the assembly and be cleaned of a previous recording and magnetized in accordance with a new recording.

A still further object of the instant invention is the provision of an economical erasing and recording head assembly for a magnetic recording device, and which assembly occupies a minimum space.

While some of the more salient features, characteristics and advantages of the instant invention have been above pointed out, others will become apparent from the following disclosures, taken in conjunction with the accompanying drawings, in which:

Figure 1 is a schematic elevational view of a portion of a magnetic recording device including an erasing head and a recording head embodying principles of the instant invention; 1

Figure 2 is an enlarged elevational view of the erasing head and recording head of Figure 1, with the casing removed, and indicating diagrammatically the electrical connections for the respective heads;

Figure 3 is an end elevational view ofthe core included in the structure of Figure 2;

Figure 4 is a fragmentary top plan view of an erasing and magnetizing head assembly of somewhat diiferent construction, illustrating diagrammatically salient electrical circuits associated with the assembly;

Figure 5 is a side elevational view of the assembly of Figure 4;

Figure 6 is an end elevational view of the structure of Figure 5;

Figure 7 is a side elevational view of an erasing and magnetizing head assembly of the character permitting the recording medium to travel in either direction and a Figure 8 is a top plan view of the structure of Figure 7 with salient associated electrical circuits indicated diagrammatically.

As shown on the drawings:

In Figure 1 I have shown an illustrated emmodiment of the instant invention operatively associated with a magnetic recording device. The

recording device includes a pair of reels or spools l and 2 between which a recording medium 3 travels, the medium being wound around the barrel of each spool. In the illustrated instance, the medium is in the form of a paramagnetic wire, a very convenient form of medium because of a high recording capacity with little bulk in comparison with paramagnetic tape or some other form of elongated member. In travelling from spool l to spool 2, the recording and reproducing direction, the medium first passes through a level wind arrangement 4 associated with a, spool i, then over a guide pulley 5, and then through a unitary erasing and reproducing arrangement, generally indicated by numeral 6. As the medium passes through the arrangement 6, the medium is cleansed of any prior recording and magnetized in accordance with a new recording. The medium then passes over another guide pulley I, through another level wind arrangement 8 and onto the reel 2. When it is desired to reproduce the recording from the medium, if the device is capable of both recording and reproduction, the medium is rewound onto the spool l, and in the rewinding operation it is necessary that the erasing head be cut out so as not to remove the last recording from the medium. The medium then travels in the original direction from the spool l to the spool 2, and the recording head acts as a pick up to reproduce the recording from the medium through a suitable amplification and speaker system not illustrated in the drawings,

the erasing head remaining out of circuit.

With reference more particularly to Figure 2, it will be seen thatthe arrangement of assembly 8 comprises both an erasing head and a magnetizing head. These two heads may, of course, be separate one from the other, but are preferably disposed relatively closely adjacent each other. In the illustrated instance, the two heads are combined in a unitary assembly in that the same paramagnetic core functions for both units. The core may be of any suitable shape, and a convenient shape is the overall substantially rectangular form as illustrated more clearly in Figure 2. V

The portion of the core functioning for the erasing head includes an outside vertical leg 9, a lower horizontal leg 10, and a top leg split as indicated at H to provide a relatively wide nonmagnetic gap and thus define confronting pole pieces I: and B on either side of the gap. The coreis completed by a middle vertical leg H which is common to both the erasing head and the recording head.

The portion of the core functioning for the recording head includes an outside vertical leg Hi, alower horizontal leg 18, and an upper leg split to provide a, relatively narrow non-magnetic gap l1 defining confronting polepieces I8 and IS on either side thereof; The magnetic circuit trated flux areas between the pole pieces in the region of both non-magnetic gaps II and I1. As seen in Figure 2, the pole pieces may be beveled or cut off obliquely at their lower ends to more effectively concentrate the flux in the vicinity of the non-magnetic gaps.

Around the leg In of the erasing head portion is a coil 2i, one end of which may be connected through a conductor 22 to a suitable high frequency oscillator, diagrammatically illustrated at 28. The other end of the coil 2! may be connected through a conductor 24 embodying a suitable switch 25 to the oscillator 23. The switch 25 is for the purpose of disconnecting the erasing head when the recording medium is being rewound after a recording has been made, to prevent the removal of that recording. The high frequency oscillator 23 may embody its own source of power, or may be connected in the usual manner to any suitable or available source or supply.

Around the leg it of the recording head Portion is a coil 26. the opposite ends of which may be connected by way of conductors 21 and 28 to an audio-amplifier and equalizer 29 which is in turn connected through conductors 30 and 31 to a microphone or equivalent pick-up device 32.

In operation, assuming that the recording medium is travelling from the spool l to the spool 2 and a recording is being made, the switch 25 is closed, and as the wire crosses the non-ma netic gap H, the high frequency flux set up by the coil 2| in the vicinity of this gap will effectively demagnetize or clean the recording medium. The course of travel of the high frequency flux set up by the coil 2! in the core is indicated very diagrammatically by dotted lines 33. Some of this flux will stray and pass through the recording head portion of the core as indicated by dotted line 34. This stray high frequency flux is suflicient to provide the desired high frequency component in the recording head. Such component will, of course, be substantially constant. Whatever sound or impulse is to be recorded upon the medium 3 will be picked up by the microphone 32, passed through the audio-amplifier 29, and thence through the coil 26 thus imposing a variable audio component on the recording head in addition to the substantially constant high frequency component, and the recording medium is very effectively magnetized to record thereon the sound or impulses desired.

As stated above, it is not essential that the recording head and erasing head be associated with the same integral core, but each may have its own individual core and be entirely separate, one from the other. It is only necessary that they are placed in sufllciently close proximity that stray high frequency flux from the erasing head will enter the recording head and provide the desired high frequency component therein.

After a recording has been made, in the event the recording device is also capable of reproducing, it is simply necessary to rewind the medium from the spool 2 onto the spool I. During this rewinding process the switch 25 is open, and the electrical switch associated wtih the recording head may also be open if desired, so that there will be no interference whatever with the recording on the medium. After the rewinding operation, the medium then may travel in its original direction from .the spool 'l to the spool 2, and during'thls course of travel the switch 25 also remains open so as not to interfere with the recording on the wire, and the recording head functions as a pick up means for the reproduction of the previously made recording. Such reproduction will of course be through any suitable amplifying circuit to a loud speaker or other device to audibly or visibly indicate the impulses recorded upon the medium 3.

In Figures 4, 5 and 6, I have illustrated a recording head and erasing :head arrangement 01' The structure of Figures 4, 5 and 6- provides cer- -tain advantages over the structure illustrated more clearly in Figure 2. The energizing coils or the equivalent are brought into closer proximity with the non-magnetic gaps so that the erasing or cleaning of the wire is a trifle more effective, and the recording is accomplished with added fidelity. Further, the construction of the arrangement is such as to resist wear due to the travel of the recording medium thereover. In the illustration for this arrangement, the recording and erasing head arrangement is shown in opposite position to that of Figure2', namely, with the erasing head to the left and the recording head to the right. In recording or in reproducing, the recording medium 3 travels from left to right as seen in Figures 4 and 5.

In this arrangement, the core is a paramagnetic block 35 having an arcuate upper edge portion as indicated at 36. The core may be laminated or solid, as may be deemed most desirable. To provide the erasing head, the core is provided with a relatively deep and comparatively wide slot 31 establishing a non-magnetic gap. At the inner end of this 'slot an aperture 38 is provided transversely through the core and of suflicient tion by virtue of the insert 4| size to establish confronting pole pieces 39 and 40 on either side of the slot. Disposed within the slot is astrip 4| of conductive material insulated in any suitable manner from the pole pieces 39 and 40. The upper face of the core or block 35 is channeled as indicated at 42 in Figure 6 and also centrally grooved as indicated at 43 to establish a path of travel for the recording medium 3. As also shown in Figure 6, the channeling of the upper edge of the core followsthe are 36. It will likewise be noted that the conductive insert 4| is channeled or cut in keeping with the upper face or edge of the core'35. The strip 4| functions substantially the same as the above described coil 2| in establishing a high frequency magnetic field through the erasing head portion of the core, but the strip 4| is much more economical to provide than is the coil 2|. The use of the strip 4| disposed within the non-magnetic gap in a core is more fully set forth and claimed in a copending application.

Opposed ends of the strip 4| may be connected by way of conductors 44 and 45 to a high frequency oscillator 46. One of these conductors may have a switch 41 therein to open the circuit throughthe erasing head during a rewinding and reproducing operation.

For the recording head, the block 35 is provided with another slot 48, comparatively narrow with reference to the erasing head slot 31. At the inward termination of the slot 48 an aperture 49 is provided to establish pole pieces 50 and 5| on either side of the slot. This slot, of course, provides a non-magnetic gap. In this non-magnetic gap a conductive insert 52 is placed, of the same general character as the previously described insert 4|. Opposite ends of the insert 5|! may be connected through conductors 53 and 54 to an audio-amplifier and equalizer 55 which is in turn connected through conductors 5B and 51 to a microphone or equivalent pickup device 58.

The operation of the structure shown in Figures 4, 5 and 6 is substantially similar to the operation of the structure described in connection with the showing in Figures 2 and 3. The high harder material than the core.

caused by the travel 6 frequency flux developed in the'erasing head porwill eflectively demagnetize or cleanse the recording medium. Spme'of this flux will stray and provide a high frequency component in the recording head portion, as above described. Having both the eras- 7 ing head and recording head energized in the immediate vicinity of the non-magnetic gaps and in the immediate vicinity of the recording medium results in somewhat better operation in that the erasing is more effective, and the recording may be accomplished with higher fidelity. The armate shape of the upper portion of the core 35 provides a greater surface of travel for the recording medium 3, which in most instances is of Thus. there is less likelihood of objectionable wear on the core of the recording medium thereover.

In Figures 7 and 8 I have illustrated still another mag'netizing head and erasing head arrangement, and in this instance the arrangement is such as to permit travel of the wire in either direction for the purpose of recording or reproducing.

In this instance, a core 53 is provided of the same general shape as the above described core 35. In the central region of this corea relatively narrow non-magnetic gap is provided and in this gap a conductive strip is inserted to provide a recording head. Opposite ends of this insert 60 may be connected by way *of conductors 6| and ,62 to an audio-amplifier and equalizer 63 which :5 to a microphone or equivalent pick up device On opposite sides of the non-magnetic gap in which the strip 60 is inserted similar but comparatively wider gaps are provided, these gaps having inserts-61 and 68 therein. Thus, an erasing head is provided on each side of the centrally disposed recording head. One end of the insert 61 may be connected through conductor 63 to a high frequency oscillator 10. The other end of the insert 60 may be connected through conductor 1| to a double throw switch 12 in turn connected by conductor 13 to the high frequency oscillator. The other insert 68 may have one end connected to conductor 69 by conductor 14, end connected by conductor 15 to the opposite terminal of the switch 1 I During a rewinding or reproducing operation, the switch 12 is left in neutral position "as illustrated in Figure 8, so that both erasing heads are de-energized. During a recording operation, assuming that the medium 3 is traveling from left to right as seen in Figure 8, the switch 12 may be closed with the conductor 1| so as to energize the left-hand erasing head, leaving the righthand erasing head de-energized. When the wire travels in the opposite direction, from right to left, and a recording is desired to be made, the switch 12 is thrown in the opposite direction to close with conductor 15 and energize the righthand erasing head, leaving the left-hand erasing head tile-energized; I

From the foregoing, it is apparent that I have provided a novel erasing head and recorder head arrangement for a magnetic recording and reproducing device, the arrangement being such that only audio current be fed to the recording head, and yet the recording head is provided with a desired high frequency component resulting from 'stray flux from the erasing head. It will be noted and its opposite cording medium may travel in either direction for recording purposes. It will be appreciated that the present invention is highly economical to use, and may be installed in extremely small s cc.

it will, of course, be understood that various details of construction may be varied through a wide range without departing from the principles of this invention and it is, therefore, not the purpose to limit the patent granted hereon otherwise than necessitated by the scope of the appended claims.

I claim as my invention:

1. In a magnetic recording device, a recording head to magnetize a recording medium in accordance with impulses to be recorded, an erasing head on each side of said recording head-each capable of demagnetizing the medium, and means to-selectively de-energize said erasing heads. an integral magnetizable core serving all three heads.

2. In a magnetic recording device, a recording head to magnetize a recording medium in accordance with impulses to be recorded, an erasing head on each side of said recording head each capable of demagnetizing the medium, means to selectively de-energize said erasing heads, means to energize each erasing head with high frequency current, means toenergize said recording head with audio current, and said recording and erasing heads being disposed sufiiciently closely together that stray high frequency magnetic flux from either erasing head will provide a useful high frequency component in the recording head.

3. In a magnetic recording device, a recording head to magnetize a recording medium in acoordance with impulses to be recorded, an erasing head on each side of said recording head each capable of demagnetizing the medium, and means to selectively de-energize said erasing heads, means to energize each erasing head with high frequency current, means to energize said recording head with audio current, and an integral magnetizable core serving all said heads.

4. In a magnetic recording device, an erasing head, a recording head, means to supply high frequency current to said erasing head, means to supply audio current to said recording head, and an integral magnetizable core serving both said heads.

5. A combination unit for a magnetic recording device, including an integral core shaped to define both a magnetizing head portion and an erasing head portion, and means for separately energizing said core portions.

6. A combination unit for a magnetic recording device, including an integral core shaped to define both a magnetizing head and an erasing head, means to impart high frequency energization to the erasing head, and means to impart only audio current to the recording head, stray flux from the erasing head providing a high frequency component in the recording head.

7. A combination unit for a magnetic recording device, including an integral core having spaced non-magnetic gaps therein one of which is wider than the other, means to energize the core around the wider gap with high frequency current, and means to energize the core around the other gap with audio current only, stray flux 8 providing a high frequency component around said other gap.

8. A combination unit for a magnetic recording device, including an integral core having spaced non-magnetic gaps therein, means to energize the core around the wider gap with high frequency current, and means to energize the core around the other gap with audio cur-.

rent only.

9. In a magnetic recording device, a recording head including a magnetizable core, means for energizing said core by audio current, means in said device energizable with high frequency current, and said core being disposed in such Proximity to the second said means that stray magneticflux will provide a useful high frequency component in said core.

10-. In a head for a magnetic recording device, a core of magnetizable material having a bounding arcuate edge, said core having a, plurality of spaced transverse slots extending inwardly from said arcuate edge to define non-magnetic gaps, said arcuate edge having a groove therein to provide a track for a travelling recording medium passing over said gaps, and means to separately magnetize said core in the vicinity of each gap. 11. In a head for a magnetic recording device, a core of magnetizable material having a bounding arcuate edge, said core having a plurality of spaced transverse slots extending inwardly from said arcuate edge to define non-magnetic gaps, said arcuate edge having a groove therein to provide a track for a travelling recording medium passing over said gaps, and means to separately magnetize said core in the vicinity of each gap, said gaps being disposed on either side of the high point of said arcuate edge.

12. In a head for a magnetic recording device, a magnetizable core having a bounding arcuate edge of a length greatly exceeding the thickness of the core transversely of said edge, said arcuate edge having a groove extending lengthwise thereof to define a track for a recording medium, said core having a transverse slot leading inwardly from said edge to provide a non-magnetic gap through which a medium following said track must pass, and means for magnetically energizing said core to cause the formation of magnetic poles of opposite polarity separated by said gap.

1 MARVIN CAMRAS.

REFERENCES CITED The following references are of record inthe file of this patent:

UNITED STATES PATENTS German 1928 

